Low temperature process for pyrolytic deposition of zirconium oxide films



Oct. 14, 1969 c. R. BARNES $472,680

LOW TEMPERATURE PROCESS FOR PYROLYTIC DEPOSITION OF ZIRCONIUM OXIDE FILMS Filed Sept. 21, 1967 United States Patent Oflice 3,472,680 LOW TEMPERATURE PROCESS FOR PYROLYTIC DEPOSITION OF ZIRCONIUM OXIDE FILMS Charles R. Barnes, Medway, Ohio, assignor to the United States of America as represented by the Secretary of the Air Force Filed Sept. 21, 1967, Ser. No. 669,657 Int. Cl. C23c 13/02 US. Cl. 117-106 8 Claims ABSTRACT OF THE DISCLOSURE Process and apparatus for depositing at 600-650 C. and at one atmosphere of pressure, the dielectric ZrO films on refractory metal alloys of molybdenum and tantalum from vaporized zirconium tetrachloride and phosphorous oxychloride with hydrogen reducing gas and nitrogen carrier gas.

CROSS-REFERENCES TO RELATED APPLICATIONS Prior related Barnes applications have now issued as Patent Nos. 3,317,342, 3,294,575, 3,294,059, 3,123,497, 3,122,450, 3,095,527 and 3,038,243.

BACKGROUND OF THE INVENTION Field of the invention The deposition from vapors of metals from their compounds with reducing gas moved through a closed system by a carrier gas.

Description of the prior art Morgan Patent No. 3,076,324 discloses a glass filament moving through vaporized A101 Zn, Cd and Mg or their oxides for acquiring depositions on the filament.

Emments et a1. Patent No. 2,162,613 discloses making a rectifier comprising a selenium electrode containing l-10 weight percent ZrCl, separated by a ZrO insulator from a conductive electrode of Bi-Cd-Sn.

SUMMARY OF THE INVENTION The nature and the gist of the invention is a. process and apparatus for transporting ZrCL, and POCl vapors with H with or Without N to a substrate at a temperature of 600- 650 C. and one atmosphere of pressure for the purpose of depositing on the substrate a dielectric film of ZrO The problem solved is the conventional comparable pyrolytic depositions of ZrO at 1,000-1,400 C. under vacuum conditions using expensive equipment. The object of this invention is the provision of a new and improved low temperature metal deposition process that does not require the use of low pressure vacuum equipment.

BRIEF DESCRIPTION OF THE DRAWING A diagrammatic apparatus for practicing the method of metal deposition that embodies the present invention is illustrated in the single figure of the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing suitable gases to be used in the process are supplied from pressurized commercially available tanks, such as from a nitrogen tank 1 and a hydrogen tank 2. The rate of gas flow from the nitrogen tank 1 is controlled by a valve 3 and is indicated by a gauge 4. The rate of hydrogen flow is controlled by a valve 5 and is indicated by a gauge 6.

The gas supply from the pressure tanks 1 and 2 are mixed and are conducted to a tank 7 containing spongy palladium catalyst 8 where any trace of oxygen contaminant in the mixed carrier and reducing gases reacts with hydrogen to form water. All of the water so formed is ad- 3,472,680 Patented Oct. 14, 1969 '11 in the bottom of the drier tank 10.

From the drier tank 10, the dried carrier and reducing gases that are free from oxygen and that have a dew point near F., are applied in common to three valves 12, 13 and 14. The three valves 12, 13 and 14 selectively connect in parallel the gas output from the drier tank 10 to a connect direct to a plating chamber 15, through a zirconium tetrachloride evaporator 16 and through a phosphorylchloride evaporator 17, respectively.

The gas flow rate between the valve 13 and the zirconium tetrachloride evaporator 16 is indicated by a flow meter 18. The gas flow rate between the valve 14 and the phosphorylchloride evaporator 17 is indicated by a flow meter 19. The temperature of the zirconium tetrachloride evaporator 16 is maintained at about 300 C. by a resistance winding 20 that is powered from a source 21. The evaporator 16 contains ZrCl, 22 which sublimes at 331 C. The temperature of the bath 23 immersing the phosphorylchloride evaporator 17 is maintained at 28 C. Positive control over the phosphorylchloride flow is afforded by the additional valve 24 before it can enter the plating chamber 15.

The plating chamber 15 contains a graphite substrate support 25 attached to the upper end of a pipe 26. The graphite substrate support 25 is maintained about in an illustrative temperature range of from 600-65-0 C. by suitable means such as by a resistance winding 27 powered from an induction heater 28, or the like. The gas input pipe 29 that extends axially of the plating chamber 15 has its discharge end at a desired proximity to a substrate disc 30 resting on top of the graphite support 25. A suitable outlet, such as a pipe 31, permits the escape of by-product gases to the ambient atmosphere or to absorbent material for entrapment, as preferred.

The process reactions here involved at or near the surface of the hot substrate 30 in accomplishing the deposition of zirconium oxide thereon and the firm adherence thereto of the zirconium oxide are:

P001: 3112 PHa 3HC1+ H2 In the event that water had previously reacted 'with the POCl to form P O Cl before reaching the substrate 30 then the involved reactions are:

( PzOgCh 8H2 2PH3 4HC1 31120 and finally the deposition of the ZrO film on the substrate by hydrolysis proceeds as:

zron 21120 ZIOg 4H0l The process of interest is applied experimentally to a thin, flat smooth disc cut from a refractory sheet metal that is under study, such for example as molybdenum of 5 mil thickness, a tantalum alloy containing 30 weight percent niobium (columbium) of 17 mils thickness or the like, that is placed on top of the graphite substrate support 25 in the plating chamber 15.

Before starting the vapor deposition, the system is flushed with nitrogen from the cylinder 1 in order to remove all oxygen from the closed system. Then hydrogen from the tank 2 is caused to enter the system and its flow rate is adjusted to 1,000 milliliters per minute as indicated by the fiow meter 6, while the rate of flow of the nitrogen is decreased to 250 milliliters per minute as indicated by the fiow meter 4.

The two gases, nitrogen and hydrogen, mix and pass through the spongy palladium catalyst 8 where any trace oxygen contaminant in the carrier gases reacts with hydrogen to form water which is subsequently adsorbed by the molecular sieve drier 9. As a result, the carrier gas 3 continues on free from oxygen and with a dew point near 90 F.

After the plating chamber 15 is flushed free of air and oxygen, the induction heater 28 is turned on and the graphite core 25 is heated to about 650 C., or to Whatever temperature is required to maintain the surface of the substrate at 625 C. The valves 12 and 13 are manipulated so that a 600 milliliter per minute portion of the carrier gas mixture flows through the evaporator 16 where zirconium tetrachloride 22 is maintained automatically at a temperature of 200 C., or at a temperature that is required to sublime the salt at the desired rate for accomplishing proper film deposition.

Simultaneously, the valves 14 and 24 are adjusted to maintain a gas flow rate of 400 milliliters per minute through the evaporator 17 which contains phosphorylchloride at room temperature of about 28 C. As a result of maintaining the designated operative conditions, fiow rates and temperatures, the reactants or the deposition on the hot substrate of a zirconium oxide film is accomplished to a depth that is proportional to the period of time the substrate is exposed to the vaporized reactant mixture of POCl P 01 ZrCl and H Films of optimum stability are produced by maintaining the zirconium oxide deposition temperature at near 625 C. Films of optimum zirconium oxide purity, freedom from entrapped phosphorous by-products, pores, etc., result from flow rates that deposit coatings of about -0.5 mil thickness per hour. The resultant films are noncrystalline, hard, adherent, transparent with a glass-like appearance and are nonconductors of electricity. The time of deposition may be decreased by increasing the pro portions in the deposition vapor of the zirconium tetrachloride and phosphorylchloride delivered to the substrate by using pure hydrogen that is not diluted with nitrogen.

It is regarded as being most significant that phosporous oxychloride or phosphorylchoride of the composition POCl and P O C1 respectively, be used in producing water by its reaction with hydrogen at the hot substrate surface. The water so produced reacts with the zirconium chloride vapor in depositing the desired film of zirconium oxide. It is interesting to note that since POCl is a dehydrating agent, which reacts with water to form P' O Cl its molecule contains no water. Therefore POCl removes any residual water from the oncoming stream of vaporized reactants before they reach the substrate, thus preventing the premature hydrolysis of the zirconium tetrachloride vapor. It also may be noted that, if preferred, water may be previously added to POCl so as to purposely increase its oxygen content and thus require less phosphorylchloride from the evaporator 17 and reduce the phosphorous compound content in the by-products that are removed by the waste pipe 31.

The transportation by hydrogen gas or by a mixture of hydrogen and nitrogen gases of mixed vapors of zirconium tetrachloride and phosphorous oxychloride at about one atmosphere of pressure, to a hot substrate maintained at about from 600-650 C. and depositing a dielectric film of zirconium oxide on the substrate is a process that is open to limited modifications in process steps, in reactant compositions, and in the stipulated physical conditions of the described environment without departing from the spirit and the scope of the present invention.

I claim:

1. The process of depositing zirconia on a substrate by applying to the substrate at a temperature of about 625 C. and a pressure of about one atmosphere a mixture in their vapor states of zirconium tetrachloride and phosphorous oxychloride.

2. The process defined by claim 1 wherein the vapors are transported to the substrate by a carrier gas selected from the group that consists of nitrogen and hydrogen.

3. The process defined by claim 1 wherein the deposition temperature is about within the range of from 600' C. to 650 C.

4. The deposition of zirconia on a substrate defined by claim 2 according to the reaction 5. The deposition on a substrate defined by claim 2 according to the reaction A P203014 8112 2PH 41101 31120 References Cited UNITED STATES PATENTS 5/1960 Richardson 23-165 X OTHER REFERENCES Powell et al., Vapor Deposition, 1966, pp. 398 to 401 relied upon.

ANDREW G. GOLIAN, Primary Examiner US. Cl. X.R. 23-21, 

